Dual circuit digital isolator

ABSTRACT

An apparatus, comprising: a substrate; a coupling capacitor that is formed over the substrate; and an isolator that is formed between the substrate and the coupling capacitor, the isolator including: (a) an MP-well layer, (b) a first well layer, (c) an epi tub layer that is nested in the MP-well layer and the first well layer, and (d) a second well layer that is nested in the epi tub layer.

BACKGROUND

As is known in the art, signal isolators can be used to transfer information across a barrier used to separate two or more voltage domains for safety or functional isolation. For example, capacitive coupling can be used to transfer information across a barrier. Optocouplers include a LED that emits light through an optically transparent insulating film and strikes a photo detector that generates a current flow that corresponds to the emitted light. RF carriers can also be used to transmit information across an isolation barrier.

SUMMARY

According to aspects of the disclosure, an apparatus, comprising: a substrate; a coupling capacitor that is formed over the substrate; and an isolator that is formed between the substrate and the coupling capacitor, the isolator including: (a) an MP-well layer, (b) a first well layer, (c) an epi tub layer that is nested in the MP-well layer and the first well layer, and (d) a second well layer that is nested in the epi tub layer.

According to aspects of the disclosure, an apparatus is provided, comprising: a substrate; a coupling capacitor that is formed over the substrate; and an isolator that is formed between the substrate and the coupling capacitor, the isolator including: (a) an MP-well layer, (b) a P-well layer, (c) an epi-tub layer that is nested in the MP-well layer and the P-well layer, and (d) an N-well layer that is nested in the epi-tub layer.

According to aspects of the disclosure, an apparatus is provided, comprising: a substrate; an isolator that is formed over the substrate, the isolator including a silicon shield layer that is formed between a first buried oxide (BOX) layer and a second BOX layer; a silicon layer having an oxide trench structure formed therein, the oxide trench structure being arranged to define a first silicon island a second silicon island; a first electronic circuit that is formed over the first silicon island; and a second electronic circuit that is formed over the second silicon island, the first electronic circuit being electrically coupled to the first electronic circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the following description of the drawings in which:

FIG. 1A is a circuit diagram of an example of a system, according to aspects of the disclosure;

FIG. 1B is a schematic cross-sectional side view of the system of FIG. 1A, according to aspects of the disclosure;

FIG. 1C is a schematic cross-sectional side view of an isolator and a coupling capacitor that are part of the system of FIG. 1A, according to aspects of the disclosure;

FIG. 1D is a partial top-down view of the isolator of FIG. 1C, according to aspects of the disclosure;

FIG. 1E is a partial top-down view of the isolator of FIG. 1C, according to aspects of the disclosure;

FIG. 1F is a top-down view of the isolator of FIG. 1C, according to aspects of the disclosure;

FIG. 1G is a top-down view of the isolator of FIG. 1C, according to aspects of the disclosure;

FIG. 1H is a schematic diagram illustrating the operation of the coupling capacitor and isolator of FIG. 1C, according to aspects of the disclosure;

FIG. 1I is a diagram of the isolator and coupling capacitor of FIG. 1C, according to aspects of the disclosure;

FIG. 2A is a schematic cross-sectional side view of an example of an apparatus, according to aspects of the disclosure;

FIG. 2B is a partial schematic top-down view of the apparatus of FIG. 2A, according to aspects of the disclosure;

FIG. 2C is a schematic top-down view of the apparatus of FIG. 2A, according to aspects of the disclosure;

FIG. 2D is a diagram illustrating the operation of the apparatus of FIG. 2A, according to aspects of the disclosure;

FIG. 3A is a schematic cross-sectional side view of an example of an apparatus, according to aspects of the disclosure;

FIG. 3B is a partial schematic top-down view of the apparatus of FIG. 3A, according to aspects of the disclosure;

FIG. 3C is a schematic top-down view of the apparatus of FIG. 3A, according to aspects of the disclosure;

FIG. 3D is a diagram illustrating the operation of the apparatus of FIG. 3A, according to aspects of the disclosure;

FIG. 4A is a schematic cross-sectional side view of an example of an apparatus, according to aspects of the disclosure;

FIG. 4B is a partial schematic top-down view of the apparatus of FIG. 4A, according to aspects of the disclosure;

FIG. 4C is a diagram illustrating the operation of the apparatus of FIG. 4A, according to aspects of the disclosure.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example of a system 100, that includes a first semiconductor device 131 and a second semiconductor device 141. The first semiconductor device 131 may be part of a high-voltage domain and the second semiconductor device 141 may be part of a low-voltage domain. The first semiconductor device 131 and the second semiconductor device 141 may be physically separated from one another by an isolation boundary 133 (e.g., an air gap or a layer of insulating material).

The first semiconductor device 131 may include an electronic circuit 101 that is formed on a substrate 135A. The substrate 135A may include a p-type substrate, a silicon-on-isolation (SOI) substrate and/or any other suitable type of substrate. The first semiconductor device 131 may also include a structure 108A and a structure 108B. The structure 108A may include a coupling capacitor 105A that is formed over an isolator 107A. The isolator 107A may be formed over the substrate 135A, as shown. The structure 108B may include a coupling capacitor 105B that is formed over an isolator 107B. The isolator 107B may be formed over the substrate 135A, as shown. As is discussed further below, the isolators 107A and 107B may be configured to reduce parasitic capacitance that is formed between plates of the coupling capacitors 105 and the substrate 135A.

The second semiconductor device 141 may include an electronic circuit 103 that is formed on a substrate 135B. The substrate 135B may include a silicon-on-isolation (SOI) substrate, a p-type substrate and/or any other suitable type of substrate. The second semiconductor device 141 may also include a structure 108C and a structure 108D. The structure 108C may include a coupling capacitor 105C that is formed over an isolator 107A. The isolator 107C may be formed over the substrate 135B, as shown. The structure 108D may include a coupling capacitor 105D that is formed over an isolator 107B. The isolator 107D may be formed over the substrate 135B, as shown. The isolators 107C and 107D may be formed on the substrate 135B, and they may be configured to reduce parasitic capacitance that is formed between the plates of the coupling capacitors 105 and the substrate 135B.

The electronic circuit 101 may include an amplifier 102, a modulator 104, and an amplifier 106. The amplifier 102 may be configured to receive a signal 171 and amplify it to produce an amplified signal 173. The modulator 104 may modulate the amplified signal 173 to produce a modulated signal 175. The amplifier 106 may amplify the modulated signal 175 to produce an amplified signal 177. The amplified signal 177 may be subsequently transmitted to the electronic circuit 103 via the coupling capacitors 105A and 105B, as shown.

The electronic circuit 103 may include an amplifier 116, a peak detector 118, a differential comparator 122, and a differential-to-single-ended signal converter 120. The amplifier 116 may be configured to receive the signal 177 via the coupling capacitors 105C and 105D and amplify the signal 177 to produce an amplified signal 179. The peak detector 118 may generate a peak signal 181, based on the amplified signal 177. The differential comparator 122 may compare the peak signal 181 to a threshold and produce a differential signal 183 that indicates whether the peak signal 181 is above or below the threshold. The differential-to-single-ended signal converter 120 may convert the differential signal 183 to a single-ended signal 185, as shown.

In some respects, the electronic circuits 101 and 103 form a system for transmission of digital signals from a high-voltage domain to a low-voltage domain, in which the digital signals are transmitted via coupling capacitors 105. The coupling capacitors 105 are formed of metal plates with dielectric insulator between. The plates of the coupling capacitors may have an undesirable parasitic capacitance to the substrates 135A/135B, which could create a loss in the signals that are transmitted from the electronic circuit 101 to the electronic circuit 103. More particularly, parasitic capacitors that are formed between the bottom plates of the coupling capacitors 105 and the substrates 135A/135B may conduct potentially large current during common mode transient immunity (CMTI) events. During such events, large amounts of current can be injected or pulled from the substrate(s) 135A/135B when large transient voltages occur differentially in the parasitic capacitors. When large amounts of current are injected or pulled from the substrate(s) 135A/135B the electronic circuit 101 and/or the electronic circuit 103 can have a non-zero substrate-to-ground impedance, and its operation may be disturbed. To reduce the effects of parasitic capacitance on the operation of the electronic circuits 101 and 103, each of the coupling capacitors 105 may be formed over a respective isolator 107.

The structure of the coupling capacitors 105 and isolators 107 is now described in further detail. FIG. 1C shows a cross-sectional side view of a structure 108 when the structure 108 is viewed from a direction Y. The structure 108 may be formed over a substrate 135. The structure 108 may be the same or similar to any of the structures 108A-D, which are discussed above with respect to FIGS. 1A-D. The substrate 135 may be the same or similar to any of the substrates 135A and 135B, which are discussed above with respect to FIGS. 1-C. According to the present example, the structure 108 includes an isolator 107 that is formed over the substrate 135, and a coupling capacitor 105 that is formed over the isolator 107. The isolator 107 may be the same or similar to any of the isolators 107A-D, which are discussed above with respect to FIGS. 1A-B. The coupling capacitor 105 may be the same or similar to any of the coupling capacitors 105A-B, which are discussed above with respect to FIGS. 1A-B.

The isolator 107 may include a PBL layer 161, a Middle P-well layer 162 (hereinafter “MP-well layer 162”, a P-well layer 163, a dielectric layer 164, an epi tub layer 165, an P-well layer 166, and a shallow trench isolation (STI) layer 167. The PBL layer 161 may be formed over the substrate 135. The MP-well layer 162 may be formed over the PBL layer 161. The P-well layer 163 may be formed over the MP-well layer 162. And the dielectric layer 164 may be formed over the P-well layer 163, as shown. The capacitor 105 may include metal layers 151 and 153 that are separated from one another by a dielectric layer 155. The metal layer 153 may be formed over the dielectric layer 164 and the metal layer 151 may be formed over the dielectric layer 155. Although in the example of FIGS. 1A-D, layers 163 and 166 are both P-well layers, alternative implementations are possible in which layers 163 and 166 are both N-well layers.

FIG. 1D shows a top-down view of the isolator 107 when the isolator 107 is viewed from a direction Z. FIG. 1D shows the isolator 107 with the dielectric layer 164, the STI layer 167, and the P-well layer 166 and removed. As illustrated in FIG. 1D, the epi tub layer 165 may be nested into P-well layer 163, such that the sidewalls 165 b of the epi tub layer 165 are in contact with the P-well layer 163.

FIG. 1E shows a top-down view of the isolator 107 when the isolator 107 is viewed from direction Z. FIG. 1E shows the isolator 107 with the dielectric layer 164, the P-well layer 163, the STI layer 167, the P-well layer 166 removed. As illustrated in FIG. 1E and FIG. 1C, the epi tub layer 165 may also be nested into MP-well layer 162, such that the sidewalls 165 b of the epi tub layer 165 are also in contact with the MP-well layer 162 and a bottom surface 165 a of the epi tub layer 165 is in contact with the PBL layer 161.

FIG. 1F shows a top-down view of the isolator 107 when the isolator 107 is viewed from direction Z. FIG. 1F shows the isolator 107 with the dielectric layer 164, and the STI layer 167 removed. As illustrated in FIG. 1F and FIG. 1C, the P-well layer 166 may be nested into the epi tub layer 165, such that a bottom surface 166 a and sidewalls 166 b of the P-well layer 166 are in contact with the epi tub layer 165.

FIG. 1G shows a top-down view of the isolator 107 when the isolator 107 is viewed from direction Z. As illustrated, the STI layer 167 may be nested into the P-well layer 166, such that a bottom surface 167 a and sidewalls 167 b of the STI layer 167 are in contact with the P-well layer 166. Furthermore, as illustrated in FIG. 1C, the sidewalls 166 b may be tapered.

FIG. 1H is a diagram illustrating the operation of the structure 108 in further detail. As illustrated, when the structure 108 is in use three equivalent (parasitic) capacitors may form that are connected in series and operate as a capacitive divider. These capacitors are herein referred to as a first equivalent capacitor C1, a second equivalent capacitor C2, and a third equivalent capacitor C3. As illustrated, the first equivalent capacitor C1 may form across STI layer 167, with charge accumulating on the metal layer 153 of the capacitor 105 and on the bottom surface 167 a of the STI layer 167. The second equivalent capacitor C2 may form across a depletion layer 191, with charge accumulating on both sides of the depletion layer 191. The depletion layer 191 may be formed at the junction between the P-well layer 166 and the epi tub layer 165. The third equivalent capacitor C3 may form across the depletion layer 193, which charge accumulating on both sides of the depletion layer 193. The depletion layer 193 may be formed at the junction between the epi tub layer 165 and the PBL layer 161.

In some respects, the STI layer 167 are disposed underneath metal layer 153 of the capacitor 105 to minimize signal loss to coupling between the capacitor 105 and the substrate 135. The addition of the STI layer 167 increases the dielectric thickness between the plates of parasitic capacitor C1, effectively reducing the coupling capacitance of parasitic capacitor C1. The addition of the STI layer 167 reduces the overall parasitic capacitance between the dielectric layer 164 and the substrate 135 by creating a series of parasitic capacitances. This in turn may increase the resistance of the system 100 to common mode transient immunity (CMTI) events. Although in the example of FIGS. 1C-H, the layer 167 is an STI layer, alternative implementations are possible in which the layer 167 is a local oxidation of silicon (LOCOS) layer or another type of field oxide layer.

FIG. 1I is a diagram of the structure 108, according to one particular implementation. In this example, the structure 108 is reverse-biased. Reverse biasing the structure 108 may include one or both of: (i) biasing the P-well layer 166 negatively with respect to the epi tub layer 165, and (ii) biasing the epi tub layer 161 negatively with respect to the PBL layer 161. If the P-well layer is biased negatively with respect to epi tub layer 165, the edge of depletion layer 191 (shown in FIG. 1H) will move further down to the epi tub layer 165 causing a reduction in junction capacitance (i.e., a reduction in the capacitance of equivalent capacitor C2). Similarly, if epi tub layer 165 is biased positively with respect to the PBL layer 161, the edge of depletion layer 193 will move further into the epi tub layer 165, causing a reduction in the capacitance of equivalent capacitor C3 (shown in FIG. 1H). To accomplish said biasing control, is necessary to provide electrical connections to the one or more the PBL layer 161, the epi tub layer 165, and the P-well layer 165. According to the example of FIG. 1G, metal contacts 197 are provided that run down to the top surface of each of the PBL layer 161, the epi tub layer 165, and the P-well layer 165. However, it will be understood that the present disclosure is not limited to any specific method for providing electrical connections to any of the PBL layer 161, the epi tub layer 165, and the P-well layer 165. In some implementations, and of the PBL layer 161, the epi tub layer 165, and the P-well layer 165 may be coupled (e.g., via contacts 197) to a power supply circuit (not shown) that is arranged to bias the layer as discussed above. The power supply circuit may be formed on the substrate 135 or provided separately.

FIG. 2A-C shows an example of a semiconductor device 200, which includes a substrate 202, a buried oxide (BOX) layer 204, a silicon shield layer 206, a BOX layer 208, and a silicon layer 210. More particularly, FIG. 2A shows a cross-sectional side view of the semiconductor device 200 when the semiconductor device 200 is viewed from a direction Y. FIG. 2B shows a top-down view of the silicon shield layer 206 when the silicon shield layer 206 is viewed from a direction Z. And FIG. 2C shows a top-down view of the semiconductor device 200 when the semiconductor device 200 is viewed from direction Z.

As illustrated in FIG. 2A, the BOX layer 204 may be formed over the substrate 202. The silicon shield layer 206 may be formed over the BOX layer 204. The BOX layer 208 may be formed over the silicon shield layer 206. And the silicon layer 210 may be formed over the BOX layer 208. As illustrated in FIG. 2B, the silicon shield layer 206 may include a first portion 206 a and a second portion 206 b that are separated from one another by an oxide isolation layer 212. Furthermore, as illustrated in FIG. 2C, a trench structure 214 including a first oxide trench 214 a and a second oxide trench 214 b may be formed in the oxide isolation layer 212. The first oxide trench 214 a and the second oxide trench 214 b may define a first silicon island 216 a and a second silicon island 216 b in the silicon layer 210. A first electronic circuit 218 a may be formed on the first silicon island 216 a and a second electronic circuit 218 b may be formed on the second silicon island 216 b. The first electronic circuit 218 a and the second electronic circuit 218 b may be coupled via a signal line 220 (and/or any other suitable type of communications channel), as shown. The signal line 220 may be used for the exchange of digital (or analog) signals between the first electronic circuit 218 a and the second electronic circuit 218 b. The first electronic circuit 218 a and the second electronic circuit 218 b may include any suitable type of electronic circuitry. For example, in some implementations, the first electronic circuit 218 a may include an electronic sensor (e.g., a pressure sensor, a magnetic field sensor, a light sensor, etc.), and the second electronic circuit 218 b may include an interface for the electronic sensor.

FIG. 2D is a diagram illustrating the operation of the semiconductor device 200 in further detail. As illustrated in FIG. 2D, when the semiconductor device 200 is in use, an equivalent capacitor C1 may be formed underneath the first electronic circuit 218 a, with charge accumulating on opposite sides of BOX layer 208. An equivalent capacitor C3 may also be formed underneath the first electronic circuit 218 a, with charge accumulating on opposite sides of BOX layer 204. The equivalent capacitors C1 and C3 may be coupled to one another, via the first portion 206 a of the silicon shield layer 206, to form a serial capacitor network 222 a.

Furthermore, when the semiconductor device 200 is in use, an equivalent capacitor C2 may be formed underneath the second electronic circuit 218 b, with charge accumulating on opposite sides of BOX layer 208. An equivalent capacitor C4 may also be formed underneath the first electronic circuit 218 a, with charge on opposite sides of BOX layer 204. The equivalent capacitors C2 and C4 may be coupled to one another, via the second portion 206 b of the silicon shield layer 206, to form a serial capacitor network 222 b. The serial capacitor network 222 a may be coupled to the serial capacitor network 222 b via the equivalent resistance R of the substrate 202.

In some respects, the configuration of the semiconductor device 200 may result in a reduced effective coupling capacitance between the circuits 218A/218B and the substrate 202, thus causing a decrease of noise cross-coupling between the first and second electronic circuits. More specifically, the layers under the first electronic circuit 218 a and the second electronic circuit 218 b form multiple serially-coupled equivalent capacitors, rather than a single equivalent capacitor, which effectively causes their total parasitic capacitance to be reduced.

FIGS. 3A-C show a semiconductor device 300 including a substrate 302, a buried oxide (BOX) layer 304, a silicon shield layer 306, a BOX layer 308, and a silicon layer 310. More particularly, FIG. 3A shows a cross-sectional side view of the semiconductor device 300 when the semiconductor device 300 is viewed from a direction Y. FIG. 3B shows a top-down view of the silicon shield layer 306 when the silicon shield layer 306 is viewed from a direction Z. And FIG. 3C shows a top-down view of the semiconductor device 300 when the semiconductor device 300 is viewed from direction Z.

As illustrated in FIG. 3A, the BOX layer 304 may be formed over the substrate 302. The silicon shield layer 306 may be formed over the BOX layer 304. The BOX layer 308 may be formed over the silicon shield layer 306. And the silicon layer 310 may be formed over the BOX layer 308. As illustrated in FIG. 3B, the silicon shield layer 306 may include a first portion 306 a and a second portion 306 b that are separated from one another by an oxide isolation layer 312. Furthermore, as illustrated in FIG. 3C, a trench structure 314 including a first oxide trench 314 a and a second oxide trench 314 b may be formed in the silicon layer 310. The first oxide trench 314 a and the second oxide trench 314 b may define a first silicon island 316 a and a second silicon island 316 b in the silicon layer 310. A first electronic circuit 318 a may be formed on the first silicon island 316 a and a second electronic circuit 318 b may be formed on the second silicon island 316 b. The first electronic circuit 318 a and the second electronic circuit 318 b may be coupled via a signal line 320 (and/or any other suitable type of communications channel). The signal line 320 may be used for the exchange of digital (or analog) signals between the first electronic circuit 318 a and the second electronic circuit 318 b. The first electronic circuit 318 a and the second electronic circuit 318 b may include any suitable type of electronic circuitry. For example, in some implementations, the first electronic circuit 318 a may include an electronic sensor (e.g., a pressure sensor, a magnetic field sensor, a light sensor, etc.), and the second electronic circuit 318 b may include an interface for the electronic sensor.

A first conductive via 332 a may be formed in the silicon layer 310 that extends from a top surface 310 a of the silicon layer 310 to a top surface 306 c of the first portion 306 a of the silicon shield layer 306. The first conductive via 332 a may be formed of any suitable type of conductive material. The first conductive via 332 a may extend through the BOX layer 308, and it may be electrically coupled to a ground source of the first electronic circuit 318 a via a ground line 334 a.

A second conductive via 332 b may be formed in the silicon layer 310 that extends from to the top surface 310 a of the silicon layer 310 to a top surface 306 d if the second portion 306 b of the silicon shield layer 306. The second conductive via 332 b may be formed of any suitable type of conductive material. The second conductive via 332 b may extend through the BOX layer 308, and it may be electrically coupled to a ground source of the second electronic circuit 318 b via a ground line 334 b.

FIG. 3D is a diagram illustrating the operation of the semiconductor device 300 in further detail. As illustrated in FIG. 3D, an equivalent capacitor C1 may be formed underneath the first electronic circuit 318 a, with charge accumulating on opposite sides of the BOX layer 304. Furthermore, an equivalent capacitor C2 may be formed underneath the second electronic circuit 318 b, with charge accumulating on opposite sides of the BOX layer 304. The equivalent capacitors C1 and C2 can be coupled to one another via the equivalent resistance R of the substrate 302. However, because the ground potentials of the first electronic circuit 318 a and the second electronic circuit 318 b are coupled to the first conductive via 332 a and the second conductive via 332 b, respectively, the parasitic capacitance of the semiconductor device 300 (which is represented by capacitors C1 and C2) will not lead to cross-coupling between the first electronic circuit 318 a and the second electronic circuit 318 b.

FIGS. 4A-B show a semiconductor device 400 including a substrate 402, a buried oxide (BOX) layer 404, a silicon shield layer 406, a BOX layer 408, and a silicon layer 410. More particularly, FIG. 4A shows a cross-sectional side view of the semiconductor device 400 when the semiconductor device 400 is viewed from a direction Y, and FIG. 4B shows a top-down view of the semiconductor device 300 when the semiconductor device 300 is viewed from a direction Z.

As illustrated in FIG. 4A, the BOX layer 404 may be formed over the substrate 402. The silicon shield layer 406 may be formed over the BOX layer 404. The BOX layer 408 may be formed over the silicon shield layer 406. And the silicon layer 410 may be formed over the BOX layer 408. A trench structure 414 including a first oxide trench 414 a and a second oxide trench 414 b may be formed in the silicon layer 410. The first oxide trench 414 a and the second oxide trench 414 b may define a first silicon island 416 a and a second silicon island 416 b in the silicon layer 410. A conductive via 432 may be formed in the trench structure 414. The conductive via 432 may extend from a top surface 414 c of the trench structure 414 to a top surface of the silicon shield layer 406. The conductive via 432 may extend through the trench structure 414, in other words. The conductive via 432 may be formed of any suitable type of conductive material.

A first electronic circuit 418 a may be formed on the first silicon island 416 a and a second electronic circuit 418 b may be formed on the second silicon island 416 b. The first electronic circuit 418 a and the second electronic circuit 418 b may be electrically coupled to one another, and to the conductive via 432, by via capacitive coupling (or another type of non-direct coupling), as indicated by the dashed arrows in FIG. 4A.

The first electronic circuit 418 a may be electrically coupled to the body of the first silicon island 416 a by a first reference signal line 434 a. The second electronic circuit 418 b may be electrically coupled to the body of the second silicon island 416 b by a second reference signal line 434 b. The first electronic circuit 418 a and the second electronic circuit 418 b may exchange digital (or analog) signals via the signal line 420. The first electronic circuit 418 a may perform active noise cancelation on a first data signal that is received over signal line 420 from the second electronic circuit 418 b. The active noise cancellation may be performed by the first electronic circuit 418 a based on a first reference signal that is received over the first reference signal line 434 a. The second electronic circuit 418 b may perform active noise cancelation on a second data signal that is received over signal line 420 from the first electronic circuit 418 a. The active noise cancelation may be performed by the second electronic circuit 418 b based on a second reference signal that is received over the second reference signal line 434 b. In some implementations, the first electronic circuit 418 a and/or first silicon island 416 a may be capacitively coupled to the silicon shield layer 406 and arranged to inject noise into that layer. When the voltage of the first electronic circuit 418 a and/or first silicon island 416 a increases abruptly, relative to the substrate 402, the first electronic circuit 418 a and/or first silicon island 416 a will capacitively pull the silicon shield layer 406 to a more positive potential. In some implementations, active circuitry within the first electronic circuit 418 a may be configured to counteract that action by generating a pulse of negative polarity that is coupled through via 432 a directly into the silicon shield layer 406 to at least partially compensate the positive pull.

FIG. 4C is a diagram illustrating the operation of the semiconductor device 400 in further detail. As illustrated, in FIG. 4C, an equivalent capacitor C1 may be formed underneath the first electronic circuit 418 a, with charge accumulating on both sides of the BOX layer 408. An equivalent capacitor C2 may also be formed underneath the second electronic circuit 418 b, with charge accumulating on both sides of the BOX layer 408. The bottom plates of equivalent capacitors C1 and C2 may be coupled to one another, via the equivalent resistances R1 and R2 of the silicon shield layer. The equivalent resistances R1 and R2 of the silicon shield layer 406 may be electrically coupled to the conductive via 432, as shown. The top plate of equivalent capacitor C1 may be coupled to the first reference signal line 434 a, and the top plate of equivalent capacitor C2 may be coupled electrically coupled to the second reference signal line 434 b.

The system may be implemented, at least in part, via a computer program product, (e.g., in a non-transitory machine-readable storage medium such as, for example, a non-transitory computer-readable medium), for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). Each such program may be implemented in a high-level procedural or object-oriented programming language to work with the rest of the computer-based system. However, the programs may be implemented in assembly, machine language, or Hardware Description Language. The language may be a compiled or an interpreted language, and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or another unit suitable for use in a computing environment. A computer program may be deployed to be executed on one computer or multiple computers at one site or distributed across multiple sites and interconnected by a communication network. A computer program may be stored on a non-transitory machine-readable medium that is readable by a general or special purpose programmable computer for configuring and operating the computer when the non-transitory machine-readable medium is read by the computer to perform the processes described herein. For example, the processes described herein may also be implemented as a non-transitory machine-readable storage medium, configured with a computer program, where upon execution, instructions in the computer program cause the computer to operate in accordance with the processes. A non-transitory machine-readable medium may include but is not limited to a hard drive, compact disc, flash memory, non-volatile memory, volatile memory, magnetic diskette and so forth but does not include a transitory signal per se.

Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that the scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims. 

The invention claimed is:
 1. An apparatus, comprising: a substrate; a coupling capacitor that is formed over the substrate; and an isolator that is formed between the substrate and the coupling capacitor, the isolator including: (a) an MP-well layer, (b) a first well layer, (c) an epi tub layer that is nested in the MP-well layer and the first well layer, and (d) a second well layer that is nested in the epi tub layer.
 2. The apparatus of claim 1, wherein the first well layer is a P-well layer and the second well layer is a P-well layer.
 3. The apparatus of claim 1, wherein the first well layer is an N-well layer and the second well layer is an N-well layer.
 4. The apparatus of claim 1, wherein the second well layer is biased negatively with respect to the epi tub layer.
 5. The apparatus of claim 1, further comprising a PBL layer that is formed between the isolator and the substrate, wherein the epi tub layer is biased positively with respect to the PBL layer.
 6. The apparatus of claim 1, further comprising an electronic circuit that is formed over the substrate, the electronic circuit being coupled to the coupling capacitor.
 7. An apparatus, comprising: a substrate; a coupling capacitor that is formed over the substrate; and an isolator that is formed between the substrate and the coupling capacitor, the isolator including: (a) an MP-well layer, (b) a first well layer, (c) an epi tub layer that is nested in the MP-well layer and the first well layer, and (d) a second well layer that is nested in the epi tub layer.
 8. The apparatus of claim 7, further comprising an electronic circuit that is formed over the substrate, the electronic circuit being coupled to the coupling capacitor.
 9. The apparatus of claim 7, wherein the isolator further includes a field oxide layer that is nested in the n-well layer.
 10. The apparatus of claim 7, wherein the isolator further includes a field oxide layer that is nested in the n-well layer and the coupling capacitor is formed over the field oxide layer.
 11. The apparatus of claim 7, wherein the field oxide layer includes a bottom surface and a plurality of sidewalls, each of the bottom surface and the plurality of sidewalls being adjacent to the epi tub layer.
 12. The apparatus of claim 7, further comprising a dielectric layer that is disposed between the isolator and the coupling capacitor.
 13. The apparatus of claim 7, further comprising a PBL layer that is formed between the isolator and the substrate. 